1. Field of the Invention
The present invention relates to a magnetic recording medium and a manufacturing method therefor, and more particularly to a magnetic recording medium which is capable of preventing deformation, such as a curl, and undesirable contact with a magnetic head and which can, therefore, be operated many times. More particularly, the present invention relates to a disc-shape recording medium which permits a high track density realizing a high linear recording density, and more particularly to a magnetic recording medium for use as an original material for flexible discs and a manufacturing method therefor.
2. Related Background Art
Hitherto, a disc-shape magnetic recording medium (hereinafter called a "magnetic disc") incorporates a non-magnetic support member made of polyethylene terephthalate and having two main surfaces on each of which a magnetic layer is formed which is made of a mixture of a polymer material and ferromagnetic power. To raise the linear recording density of a magnetic disc of the foregoing type, an attempt has been made to reduce the track width.
To raise the linear recording density of the magnetic disc for use in the magnetic disc drive, the distance from a magnetic head to the magnetic disc has been reduced.
The conventional magnetic disc drive, however, suffers from a problem of deformation of the magnetic disc which must be overcome to pursue development in order to raise the linear recording density. The conventional magnetic disc drive easily encounters a tracking error and rise in the error rate if the magnetic disc is deformed. As a result, the linear recording density of the magnetic disc cannot easily be raised.
To overcome the deformation and change in the dimension occurring during reservation of the magnetic disc, a method of manufacturing a magnetic disc has been disclosed in Japanese Patent Laid-Open No. 62-124630. The disclosed manufacturing method will now be described.
The foregoing manufacturing method has steps of winding an original material for manufacturing magnetic recording mediums into a roll shape; subjecting roll-shape original material for manufacturing the magnetic recording mediums to a heating process for the purpose of enhancing reactions of a binder and a crosslinking material in the magnetic layer; and unwinding the roll-shape original material for manufacturing the magnetic recording mediums into a sheet shape; and punching the sheet-shape material into disc shapes.
That is, the foregoing method is a method having the steps of subjecting the magnetic recording medium wound into the roll shape to the heating process for activating the binder and the crosslinking material in the magnetic layer to increase the strength of the magnetic layer; and punching the original material for manufacturing the magnetic recording mediums into disc shapes. Therefore, the magnetic disc obtained by the punching process has the increased strength. Thus, deformation and undesirable change in the dimension can satisfactorily be prevented.
The foregoing method, however, suffers from the following problems. That is, the original material for manufacturing the magnetic recording mediums in a state in which the original material has been wound into the roll shape is subjected to the heating process. Therefore, deformation of the original material of the magnetic recording medium when it is wound causes the original material of the magnetic recording medium to be warped when it is rewound into a sheet shape, that is, curled. A portion of the original material of the magnetic recording medium wound tightly into the roll shape is deformed when the original material is rewound into the sheet. Another problem arises in this case in that the characteristic of the surface of the magnetic layer deteriorates.
A magnetic disc manufactured by punching, into the disc shape, the original material of the magnetic recording medium having deformation, such as a curl, is deformed. As a result, the contact with the magnetic head becomes nonuniform. If the magnetic disc is operated many times, the magnetic layer is worn excessively. Thus, the magnetic disc cannot smoothly be rotated when a recording operation or a reproducing operation is performed. As a result, there arises a problem of unsatisfactory durability and deterioration in the recording/reproducing characteristic.
To overcome the above-mentioned problems, a contrivance has been suggested which has a structure that the coefficient of thermal contraction of a non-magnetic support member is controlled to satisfactorily prevent deformation of the original material of the magnetic recording medium occurring by dint of heat. Thus, deformation of the magnetic disc is attempted to be prevented.
However, the above-mentioned conventional contrivances for preventing deformation cannot attain a satisfactory effect. Thus, deformation of the magnetic disc cannot completely be prevented after the magnetic disc has been preserved or after the magnetic disc has been subjected to heat treatment.